Tire having an H/S form ratio of <0.6

Abstract

A tire, the H/S form ratio of which is at most 0.6, formed radially from the inside to the outside by a triangulation ply of metal cables oriented at least 60°, two working crown plies formed of inextensible metal cables oriented at angles of between 10° and 45°, between which there is inserted a first additional ply of metallic elements which are oriented substantially parallel to the circumferential direction of the tire, a second additional ply being arranged, on either side of the tire, radially above the outermost working ply and substantially centered on the end of the first additional ply.

I claim:  
     
       1. A tire comprising a radial carcass reinforcement ( 1 ) surmounted by a crown reinforcement ( 3 ) comprising at least two working crown plies ( 32 ,  34 ) of inextensible cables, crossed from one ply to the next, forming angles (α, β) of between 10° and 45° with the circumferential direction, said plies having widths L 32 , L 34  at least equal to 80% of the maximum axial width S 0  of the carcass reinforcement and including, firstly, between the carcass reinforcement and the working ply ( 32 ) radially closest to the axis of rotation, an axially continuous ply ( 31 ) formed of inextensible metal cables forming with the circumferential direction an angle δ of at least 60° and the axial width L 31  of which is at least equal to the axial width L 32 , L 34  of the narrowest working crown ply ( 32 ,  24 ), and including, secondly, between the two working crown plies, a first additional ply ( 33 ) formed of metallic elements oriented substantially parallel to the circumferential direction, the axial width L 33  of said first additional ply being at least equal to 0.7 S 0 , and the modulus of elasticity upon traction of which is at most equal to the said modulus of the most extensible working ply ( 33 ,  34 ), characterized in that there is arranged, radially above the radially outermost working crown ply ( 34 ) and on either side of the tire, a second additional ply ( 36 ) formed of metallic elements oriented substantially parallel to the circumferential direction, of narrow width L 36  substantially centered on the end of the first additional ply ( 33 ) such that the ends of said second additional ply are axially distant from each end of the first additional ply by at least 10 mm and such that said second additional ply radially covers the end of the first additional ply of circumferential cables which is arranged between the two working plies. 
     
     
       2. A tire according to  claim 1 , characterized in that the modulus of elasticity upon traction of the second additional ply is equal to the said modulus of the same name of the first additional ply. 
     
     
       3. A tire according to  claim 2 , characterized in that the common modulus of the additional plies is low for a relative elongation of between 0% and 0.4%, and at most equal to the greatest modulus of elasticity upon traction of the most extensible working ply, for relative elongations greater than 0.4%. 
     
     
       4. A tire according to  claim 3 , characterized in that the additional plies are formed of elastic cables, having a curve of tensile stress as a function of the relative elongation which has shallow gradients for the slight elongations of between 0 and 0.4% and a steep and substantially constant gradient for the greater elongations. 
     
     
       5. A tire according to  claim 3 , characterized in that the additional plies are formed of cables oriented circumferentially and cut so as to form sections of a length very much less than the circumference of the least long ply, the cuts between sections being axially offset relative to each other. 
     
     
       6. A tire according to  claim 1 , characterized in that the crown reinforcement furthermore comprises, radially furthest to the outside, a protective ply ( 35 ), formed of elastic cables forming an angle of the same direction and substantially the same value as the angle of the subjacent working ply ( 34 ) with the circumferential direction, and in that the second additional ply ( 36 ) has a width of between 15 and 50 mm, said second additional ply ( 36 ) axially extending the protective ply ( 35 ), and said extension being produced leaving only a gap of less than 5 mm between the axially inner end of the second additional ply and the axially outer end of the protective ply of elastic cables.